I try to carry less than 10, usually 6- 8 discs.
Drivers- Champion sidewinder,Star leopard,DX Cheetah-rhbh
Drivers-DX Wraith,Discraft Flick-sidearm
Midrange-Discraft Impact,Discraft Meteor
Putters/approach-Innova Spider.
Could probabley play with 3. Flick[ sidearm], Sidewinder[backhand,and the Spider for approach/putting.
The summers here in Georgia are brutal. You can't carry enough water, and carring more than 6/ 8 discs gets heavy on this old guy.

I regularly carry 13 discs, but there is usually 1-2 more testers kicking around the bag. I'll put a new disc in or bring one out of storage and take second throws throughout the day (no, I don't do it when there are people behind me). If I find it fills a niche better than one I have, it finds a home. I've been playing about a year, and I'm still buying everything in sight. I would say that there is about 6-8 discs that I would never play without.